Acoustic wave devices are used as a filter, a duplexer or the like included in mobile communications terminals. As acoustic wave resonators, there are a surface acoustic wave (SAW) resonator using a surface acoustic wave, a boundary acoustic wave resonator using a boundary wave, a Film Bulk Acoustic Resonator (FBAR) using a piezoelectric thin film and the like. A functional element which excites an acoustic wave is an electrode such as an IDT (Inter Digital Transducer) in the surface acoustic wave device for example, and is a region in which electrodes sandwiching a piezoelectric thin film overlap in the FBAR. In the acoustic wave device, to excite the acoustic wave effectively, there is a case that an air-space is formed above an acoustic wave element.
For example, Japanese Patent Application Publication No. 2008-227748 discloses an invention in which an acoustic wave element is sealed with a strengthening layer made of an epoxy resin and a metal so that a space is formed above an acoustic wave element. Japanese Patent Application Publication No. 2010-157956 discloses an invention in which an acoustic wave element is sealed with a top panel made of copper. Japanese Patent Application Publication No. 9-326447 discloses an invention in which an acoustic wave element is sealed with a thermoplastic resin.
However, when a ceiling made of metal (metal ceiling) located above the functional element is connected to ground, characteristics of the electronic component are degraded.